JP3728609B2 - Focus detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a focus detection apparatus for multi-focus detection or multi-range measurement.
[0002]
[Prior art]
Conventionally, as a focus detection device used in cameras and the like, a so-called multi-range focus detection device has been proposed that can measure not only the area near the optical axis of the taking lens but also the area outside the optical axis at the same time. Has been. In this method, a plurality of focus detection optical systems for measuring the distance of one area are arranged by the number of areas. Japanese Patent Application Laid-Open No. 3-249718 proposes a focus detection apparatus that includes a plurality of focus detection optical systems and enables focus detection at four points in the screen as shown in FIG. j1 is a central area, j2 is an upper area, j3 is a right area, and j4 is a left area. FIG. 6 shows the configuration. The light beam transmitted through the photographing lens L enters the secondary imaging lens L2 through the semi-transmissive mirror M1, the sub-mirror M2, the field mask SM, the field lens L0, the reflection mirror M3 and the aperture mask AM, and reaches the line sensor CS.
[0003]
FIG. 7 is a sectional view of the focus detection apparatus having the configuration shown in FIG. Since the field mask SM needs to be disposed in the vicinity of the primary image plane F conjugate with the film surface, the field mask SM and the field lens L0 are disposed near the bottom surface T of the mirror box. Then, since the surface Lh of the field lens L0 is exposed to the bottom surface of the mirror box through the opening S1 of the field mask SM, the light transmitted through the photographing lens is reflected on the surface Lh of the field lens and reflected on the film surface. A so-called ghost phenomenon may occur. For example, as shown in FIG. 7, the light ray g1 entering from the opening S1 of the field mask corresponding to the central area is reflected by the surface Lh of the field lens, and comes out of S1 and reaches the film surface. .
[0004]
As a countermeasure against such a ghost in the optical path, Japanese Patent Application Laid-Open No. 60-60615 proposes a method of arranging a light shielding cylinder between a field mask and a sub mirror. FIG. 8 shows a cross-sectional view thereof. Apart from the field mask 41, a light shielding plate 42 having a light shielding cylinder portion 42a is arranged in front of the field mask. Since the light-shielding tube portion 42a limits the light beam g2 incident on the field lens 40 and the g3 reflected by the field lens 40 and traveling toward the film surface, ghosting is prevented.
[0005]
[Problems to be solved by the invention]
However, the ghost prevention by the light shielding cylinder has the following problems. That is, since a certain length is required for the tube portion, the length between the tip 42a1 of the light shielding tube and the field mask 41, which is almost the same height as the bottom surface of the mirror box, is increased. The tip 42a1 of the light-shielding cylinder portion needs to be lowered to almost the same height as the bottom surface of the mirror box so that the regular light flux on the film surface is not vignetted. Therefore, the field mask and the field lens are lowered accordingly by arranging the light-shielding cylinder. As a result, the camera becomes larger. In addition, since the field mask and the field lens are separated from the primary image plane, the accuracy of focus detection is affected, for example, stray light increases.
[0006]
In the case of multi-area focus detection, light incident from the opening of the field mask corresponding to one area is reflected on the surface of the field lens and exits from the opening of the field mask corresponding to the adjacent area. There is a ghost light toward The optical path is shown in FIG. The light ray g4 incident from the opening S1 in the central area is reflected by the surface Lh of the field lens, and exits from the opening S2 in the upper area toward the film surface. In such an optical path, in particular, when trying to prevent the light beam entering from the portion S1a on the opening S2 side of the opening S1 and exiting from the portion S2b on the opening S1 side of the opening S2 with the light shielding cylinder, as in g5. The height d to the tip of the light-shielding cylinder is longer than that in the same area opening in FIG. 7 because the distance m between the two openings is larger. Accordingly, there is a problem that the size of the entire camera is increased and the focus detection accuracy is lowered accordingly.
[0007]
The present invention has been made in view of the above problems, and an object of the present invention is to shield ghost light without increasing the distance between the field mask and the bottom surface of the mirror box.
[0008]
[Means for Solving the Problems]
In order to achieve this object, the focus detection apparatus of the present invention is provided with a plurality of focus detection optical systems that re-image a subject image on a line sensor by a secondary imaging lens and detect the focus state of the photographing lens. In a focus detection apparatus for detecting a focus detection state in a plurality of areas in a photographing screen, a field mask (SM) having a plurality of openings defining an area disposed in the vicinity of the imaging surface of the subject image , and a field mask In the vicinity of (SM), a plurality of field lenses (L0) arranged between the field mask (SM) and the secondary imaging lens, and between the field mask (SM) and the field lens (L0) are provided. And a light shielding plate (2) substantially perpendicular to the field mask (SM).
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0010]
FIG. 1 is a sectional view showing an embodiment of a focus detection apparatus according to the present invention.
[0011]
In FIG. 1, the field lens L 0 and the field mask SM are fixed to the holder 1. Between the field lens L01 in the central area and the field lens L04 in the upper area, the field lens L01 is substantially perpendicular to the field mask SM in a place where normal light for focus detection from the opening of the field mask SM is not vignetted. The light shielding plate 2 is arranged substantially parallel to the boundary line 5 between L04 and L04. The shape of the light shielding plate 2 is shown in FIG. The end face 2a on the field mask SM side is a straight line so as to be in close contact with the back surface of the field mask SM, and the end face 2b on the field lens L0 side has an arc shape along the spherical surface of the lens. Thereby, there are no gaps between the light shielding plate 2 and the field mask SM and the field lens L0, and the ghost light is shielded. The light shielding plate 2 is fixed to the holder 1 by bending both ends 2c and 2d of the light shielding plate 2 as shown in FIG. 2, and inserting the bent portion into the gap between the side surface of the field lens L0 and the inner wall of the holder 1. What is necessary is just to fix to the inner wall of this by adhesion | attachment etc.
[0012]
FIG. 3 shows an example in which the light shielding plate is configured as a part of the field mask SM. When configuring the central area opening S1 of the field mask SM, the end surface on the upper area opening S2 side is bent so as to be bent to the field lens L0 side, and the bent portion functions as a light shielding plate as it is. The shape of the tip 2e of the cut and bent portion is also an arc shape so as to follow the spherical surface of the lens L0, so that a gap with the surface of the field lens L0 is not generated.
[0013]
In addition, in the Japanese Patent Application Laid-Open No. 7-191258, the present applicant has proposed that a field lens is divided to provide a gap in order to prevent stray light in a multi-area focus detection device. When the field lenses corresponding to the two areas where ghost light is generated are divided in this way, the light shielding plate 2 is disposed by simply inserting it into the gap between the field lenses L01 and L04 as shown in FIG. Can be assembled easily. In this case, the end face of the light shielding plate 2 does not need to be aligned with the spherical surface of the field lens L01 or L04.
[0014]
【The invention's effect】
As described above, according to the focus detection apparatus of the present invention, the light shielding plate (2) substantially perpendicular to the field mask (SM) is provided between the field mask (SM) and the field lens (L0). Therefore, it is possible to shield the ghost light without increasing the distance between the field mask and the bottom surface of the mirror box, that is, without increasing the size of the camera or reducing the focus detection accuracy.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a first embodiment of the present invention.
FIG. 2 is a plan view showing the shape of a light shielding plate in the first embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a second embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a third embodiment of the present invention.
FIG. 5 is a plan view showing the arrangement of multi-focus detection areas.
FIG. 6 is a perspective view illustrating a configuration of a multi-focus detection apparatus.
FIG. 7 is a cross-sectional view showing a conventional multi-focus detection apparatus.
FIG. 8 is a cross-sectional view showing a conventional shielding tube for preventing ghost light.
FIG. 9 is a cross-sectional view illustrating an optical path of ghost light in the multi-focus detection apparatus.
[Explanation of symbols]
L01 to L04 Field lens SM Field mask S1, S2 Field mask opening 1 Holder 2 Light shielding plate

Claims (4)

A plurality of focus detection optical systems for detecting a focus state of the photographing lens by re-imaging a subject image on a line sensor by a secondary imaging lens to detect a focus detection state in a plurality of areas on the photographing screen. In the focus detection device,
A field mask having a plurality of openings defining the area arranged in the vicinity of the imaging surface of the subject image ;
A plurality of field lenses disposed between the field mask and the secondary imaging lens in the vicinity of the field mask;
A focus detection apparatus comprising: a light shielding plate provided between the field mask and the field lens and substantially perpendicular to the field mask. 2. The light shielding plate according to claim 1, wherein one end has a shape along the surface of the field mask on the field lens side, and the other end on the opposite side has a shape along the lens surface of the field lens. The focus detection apparatus described in 1. The focus detection apparatus according to claim 1, wherein the light shielding plate is configured integrally with the field mask in a shape obtained by cutting and bending a part of the field mask. The focus detection apparatus according to claim 1, wherein there is a gap between the plurality of field lenses, and the light shielding plate is inserted into the gap.

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